An excellent "How To ..." http://www.apug.org/forum/index.php?...cus-screen.54/
An excellent "How To ..." http://www.apug.org/forum/index.php?...cus-screen.54/
I decided to do the following test:
I ground 2 glasses with 400 grit last night. I will grind one of them with 800 grit then use my D70 on manual mode to compare the brightness of the two screens.
Science is what we understand well enough to explain to a computer. Art is everything else we do.
--A=B by Petkovšek et. al.
I've ground different sizes of glass, from 5x7 to 16 x 20. I start with 25 micron, then 12, then 5. Sometimes I go down to 3 microns but haven't done any testing to see the difference between the 5 and 3.
Using this method is faster than when I tried to use the 5 as a starting point with a much more consistent grind over the entire surface.
Hi Jim, I'm not worried about depth of field but evenness of granularity/diffusion. Maybe my last batch of glass was wavier than most.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
Quite a few years ago, I made an 8X10 replacement glass for my Cambo. I used a good-sized (12"X12"?) piece of flat marble as my base, and spread the grit slurry over its surface.
The glass I used was regular window glass cut to size, with clipped corners. I don't recall which combination of grits were used.
I used suction cups (lever-action towel hangers) to grip the glass, and within an hour, had a beautiful (to me) groundglass, which served well until I received
a Yankee replacement.
It also did a nice job of polishing the marble.
All I missed were the gridmarks on the original ( and on the Yankee replacement); the focussing brightness and accuracy were excellent.
One way to make neat unobtrusive grids on a ground side of a ground glass is to scribe them with a hard fairly sharp tool. A sewing needle, old style phonograph needle, or ice pick might work. The pattern for the lines is visible through the GG. Use a straight edge to guide the tool.
I ground one 400, one 600, and one with 400-then-800.
I conclude that 400 is too coarse. The two finished with finer grits are hard to distinguish. I further conclude that on small pieces of glass, starting with 400 is a waste of time vs. just jumping to 800 or 600.
Another aspect is my 400 I bought from The Rock Barrell in Dallas and it's black. The 600 and 800, although also supposedly SiC, is from a different vendor, green, and probably top quality.
Science is what we understand well enough to explain to a computer. Art is everything else we do.
--A=B by Petkovšek et. al.
The source matters. I have some 1 micron aluminum oxide, which is finer than my usual grit, but it must be contaminated, as any screen made with it gets huge scratches.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
Here is a picture I took with my cellphone through my loupe of the two glasses butted up against each other on the back of my camera. You can see the finer one on the right is both brighter and less grainy.
Science is what we understand well enough to explain to a computer. Art is everything else we do.
--A=B by Petkovšek et. al.
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